The use of a top blown rotary converter for the conversion of sulfide concentrates to recover non-ferrous metals such as copper, nickel, lead, cobalt and the like has become a significant means for such conversion. In use of such converters, sometimes known as Kaldo converters, the sulfides are smelted and the non-ferrous metals reduced using oxygen or oxygen-containing gases to convert sulfides to SO.sub.2 with surface blowing by means of a lance.
The use of a top blown rotary converter in conversion of sulfide concentrates has been described in the article "TBRC A New Smelting Technique" by R. A. Daniele and the present inventor, presented at the 1972 AIME Annual Meeting, San Francisco, Calif. Feb. 20-24, 1972, and in the article "Full Scale TBRC Smelting Tests on Copper Concentrate" by said authors, presented at the 1974 AIME Annual Meeting, Dallas, Tex. Feb. 24-28, 1974, the contents of said articles being incorporated by reference herein.
When pure oxygen is used to produce, for example, blister copper from copper concentrates, the oxidation of the iron and sulfur present in the concentrates produces more heat than is consumed in the process. This excess heat must be either absorbed or removed in some manner so as to prevent excess temperatures from developing in the converter.
Methods have been proposed for removal of excess heat developed during conversion of concentrates in a top blown rotary converter such as (1) the dilution of the oxygen by use of air-oxygen mixtures with the nitrogen content of the air absorbing excess heat, (2) the injection of liquid water directly into the converter, or (3) the charging of copper scrap which is melted with the excess heat. This latter method is well suited to absorption of the heat but, unfortunately, sufficient scrap is rarely available at the converter site. The other two methods described, while absorbing the heat, have the disadvantage of excessive dilution and contamination of the exhaust gases discharged from the converter. If sulfuric acid is to be made, the water vapor must be removed and, if sulfur dioxide is to be recovered, or elemental sulfur is to be produced, from the exhaust gases, considerable more energy will be required because of the dilution of the exhaust gases. While dilution of the oxygen with sulfur dioxide would result in reduction of the impurities in the exhaust gas, this requires a high recycle volume.
In the present invention, sulfur trioxide is used as a diluent for the oxygen-containing gas charged to the converter, with the advantages of reducing the dilution of sulfur dioxide in the exhaust gas, providing a source of oxygen by the decomposition of sulfur trioxide to sulfur dioxide in the converter under operating conditions, and providing a high heat absorbing capacity that is approximately four and one-half to five times that of an equal volume of nitrogen and two and one-half to three times that of sulfur dioxide with resultant lower recycle volume, as well as subsequent recovery of heat from the system, through subsequent catalytic oxidation of sulfur dioxide to sulfur trioxide, for production of high pressure steam.